1. Field of the Invention
The present invention relates to a rotary pump for sucking and discharging fluid and a braking apparatus using the rotary pump. In particular, the present invention is preferably applied to an internal gear pump such as a trochoid pump or the like.
2. Description of Related Art
There is a trochoid pump as one type of an internal gear rotary pump. FIG. 22 shows such a trochoid pump. As shown by the drawing, the trochoid pump is constituted by an inner rotor 701 having an outer teeth portion 701a at its outer periphery, an outer rotor 702 having an inner teeth portion 702a at its inner periphery, a casing 704 for containing the outer rotor 702 and the inner rotor 701. The inner rotor 701 and the outer rotor 702 are arranged in the casing 704 in a state where the inner teeth portion 702a and the outer teeth portion 701a are in mesh with each other and a plurality of gap portions 703 are formed by the respective teeth.
When a line running on respective central axes X' and Y' of the outer rotor 702 and the inner rotor 701 is defined as the center line Z' of the pump, an intake port 705 and a discharge port 706 respectively communicating with the plurality of gap portions 703 are formed on both sides of the center line Z'. When the pump is driven, the inner rotor 701 rotates with the central axis Y' as a drive axis. In accordance therewith, the outer rotor 702 also rotates in the same direction by mesh between the outer teeth portion 701a and the inner teeth portion 702a. In this case, each of the gap portions 703 changes from a large volume to a small volume and vice versa during a time period in which the outer rotor 702 and the inner rotor 701 make one turn. Due to that volume change, oil is sucked from the intake port 705 and discharged to the discharge port 706.
In the internal gear pump such as a trochoid pump operating in this way, oil may leak from a clearance between the outer rotor 702 and the inner rotor 701. The oil leakage is caused since the outer rotor 702 is separated from the inner rotor 701 and a clearance is produced at a gap portion of which the volume becomes its maximum among the plurality of gap portions 703 owing to a pressure difference between discharge pressure and intake pressure.
The gap portion of which the volume becomes its maximum, is a closed gap portion which communicates neither with the intake port 705 nor the discharge port 706. Therefore, it maintains the pressure difference between the discharge pressure and the intake pressure and plays an important role in the pump smoothly carrying out intake and discharge operations. Accordingly, when the oil leakage as mentioned above happens, smooth pump operation cannot be carried out. For example, there arise problems such that a rotating unit is locked and high pressure oil cannot be discharged.
Hence, according to, for example, Japanese Unexamined Utility Model Publication No. JP-U-5-6170, oil leakage is prevented by reducing the clearance between the outer rotor 702 and the inner rotor 701.
Specifically, a clearance L1 between the outer rotor 702 and the casing 704 at a vicinity of the position where the volume of the gap portion becomes its maximum, is made smaller than a clearance L2 between the outer rotor 702 and the casing 704 at a vicinity of the closed gap portion (having minimum volume) opposed to the closed gap portion having the maximum volume. As a result, the clearance between the outer rotor 702 and the inner rotor 701 at the closed gap portion having the maximum volume is prevented from widening. However, in this case, because of high pressure fluid leaking from the discharge port 706 to the outer periphery of the outer rotor 702, the outer rotor 702 is pushed to a portion of the inner face of the casing 704 (point P) on the right side of the drawing.
Generally, the outer rotor 702 and the inner rotor 701 have fabrication errors in fabrication steps. Therefore, heights (length in diameter direction) of the teeth of the inner teeth portion 702a and heights (length in diameter direction) of the teeth of the outer teeth portion 701a are different from each other, respectively. Therefore, in setting clearances among a drive shaft, the inner rotor 701, the outer rotor 702 and the casing 704, the clearances are set by, for example, a method in which a maximum height tooth of the inner teeth portion 702a engages with a maximum height tooth of the outer teeth portion 701a.
However, as mentioned above, heights of the teeth of the inner teeth portion 702a and the heights of the teeth of the outer teeth portion 701a are different from each other, respectively. Accordingly, when the closed gap portion having the maximum volume is formed by a tooth of the inner teeth portion 702a and a tooth of the outer teeth portion 701a which are shorter than the respective maximum height teeth thereof, a clearance is produced between the inner teeth portion 702a and the outer teeth portion 701a at the closed gap portion and oil leaks from the clearance.
Further, when the discharge pressure becomes high, force pushing the outer rotor 702 to the portion of the inner face of the casing 704 (vicinity of point P) on the right side of the drawing becomes large. Therefore, the pump may not be driven smoothly or the driving of the pump may be impossible since the outer rotor 702 are locked by being squeezed by the the casing 704 and the inner rotor 701.